The cytokine tumor necrosis factor α (“TNF-α”) has a broad spectrum of biological activities. TNF-α is produced by activated macrophages and a variety of other cells, including antigen-stimulated T cells, activated mast cells and activated natural killer cells. TNF-α is initially produced as a transmembrane protein of about 25 kD. A 17 kD fragment of this membrane protein is proteolytically cleaved from the cell membrane and circulates as a 51 kD homotrimer. TNF-α mediated processes proceed via the interaction of this trimeric protein with a receptor protein at the surface of a target cell.
TNF-α plays an important role in coordinating the body's response to infection, and serves as an important mediator of inflammation. For example, TNF-α signaling has been implicated in the induction of fever and the production of interferon-γ by T cells. TNF-α induces increased binding of leukocytes to endothelial cells, resulting in accumulation of leukocytes at sites of infection. TNF-α signaling has also been implicated in inducing the production of interleukin-1 and prostaglandins by macrophages, and is involved in the breakdown of the extracellular matrix, inducing collagenase in synoviocytes, and in bone resorption via osteoclast activation.
TNF-α has certain effects on the growth and metastatic potential of tumors. For example, certain human tumor cell lines are sensitive to TNF-α in vitro and TNF-α activation may precede killing of tumor cells by macrophages.
High levels of TNF-α are generally associated with chronic immune or inflammatory diseases, and are considered a cause of neural and cellular degeneration. At lower levels, however, TNF-α plays an important role in the cell life cycle, cellular response to foreign attack, and maintenance of homeostasis. For this reason, it will be appreciated that the purpose of this invention is not the complete and absolute inhibition of TNF-α, but rather the modulation of the cellular response to TNF-α levels and the treatment of TNF-α mediated conditions, thereby permitting an effective treatment for the chronic immune and inflammatory responses that occur when excess TNF-α is produced.
The production of TNF-α has been implicated in a variety of disease states including but not limited to the following: septic shock; endotoxic shock; cachexia syndromes associated with bacterial infections, such as tuberculosis and meningitis; viral infections, such as AIDS; parasitic infections, such as malaria; neoplastic disease; autoimmune disease, including some forms of arthritis, especially rheumatoid and degenerative forms; and adverse effects associated with treatment for the prevention of graft rejection. Thus, there is a need for agents which can interrupt or modulate the TNF-α signaling process.